Pneumatic tools offer a “best-fit” solution in many applications because of their safety, reliability, and simplicity. Typically, however, pneumatic tools for impacting a workpiece by delivering hammering blows, e.g., pneumatic hammers, have characteristics that detract from their utility or preclude their use in some applications such as breaking off casting risers on a production line, or seating large press-fit assemblies.
A pneumatic tool for impacting a workpiece by delivering hammering blows, whether percussive or single stroke, is normally designed to produce an impact via a slidable impactor device. Typically, the impactor device comprises a tool bit that is held against a workpiece before impact and a piston for impacting the tool bit and transferring kinetic energy through the tool bit to the workpiece to perform the necessary work. The travel of the tool bit is fairly short and constrained by the workpiece. The kinetic energies developed in the impactor device are primarily absorbed by the workpiece. Any residual kinetic energies are usually small and dissipated in tool components with the help of springs or elastic pads, if necessary, to moderate the resulting forces. However, some applications, such as breaking off casting risers on a production line, require the impactor device to carry high kinetic energy throughout a relatively long stroke to impact workpieces at varying distances. Residual kinetic energies, and the forces from their dissipation, can be quite high. In these types of applications, an energy absorbing mechanism is necessary to dissipate high kinetic energies from the impactor device without the subsequent destruction of other tool components, especially in the event of a dry fire, in which the pneumatic tool is actuated with the tool bit being improperly positioned relative to the workpiece. In such an event, without an energy absorbing mechanism, tool components can be subjected to large destructive forces.
One example of such an energy absorbing mechanism in a pneumatic tool is shown in U.S. Pat. No. 6,364,032 issued to DeCord, Jr. et al. DeCord, Jr. et al. discloses a pneumatic tool having an elongated casing defining a chamber. An impactor device is slidable within the chamber along an operational axis. A valve system slides the impactor device within the chamber by selectively introducing and releasing pressurized fluid into and out from the chamber. An energy absorbing mechanism is slidably supported within the chamber for dissipating the kinetic energy of the impactor device. The energy absorbing mechanism comprises a nylon disc and a pressure chamber between the nylon disc and a distal end of the elongated casing. A pressurization valve pressurizes the pressure chamber. The nylon disc slides against pressurized fluid in the pressure chamber upon impact by the impactor device to dissipate kinetic energy of the impactor device. The nylon disc is continuously subjected to hammering impacts from the impactor device without any prior or subsequent dissipation of kinetic energy by the energy absorbing mechanism. Thus, in the event of a dry fire, any kinetic energy in the impactor device must either be absorbed by the nylon disc and the pressurized fluid in the pressure chamber, or by other components of the tool.